The invention relates to a television transmission or data storage system comprising at least one data generator, at least one data receiver and a transmission or data storage channel arranged between the generator and the receiver, said data generator for supplying two essentially different picture signals being provided with a first signal source for supplying a signal comprising luminance information during a first part of a line period of the data generator, and with a second signal source for supplying a signal comprising luminance information during a second part of the line period of the data generator, the data generator being furthermore provided with an encoding circuit for a time-division multiplex encoding of the said signals comprising information and of signals comprising synchronizing and identification information, said encoding circuit having an output for supplying a time-division multiplex encoded signal for transmission via the transmission channel or storage in the data storage channel, the data receiver comprising a decoding circuit coupled to the said channel having a substantially adapted operation to that of said encoding circuit for supplying signals comprising luminance information which largely corresponds to the data produced by the signal sources in the data generator. The invention also relates to a data generator and receiver suitable for use with such a television system.
A system of this type is known for British Patent Application No. 2,140,242 (PHN 10,986) in the name of the Applicant. In this Application (see FIGS. 2d and 2e) a plurality of variants of a television system is described in which the luminance information of two different pictures is transmitted or stored. The two signals comprising the picture information are time-compressed by a time-compression factor which is equal to 0.5 for both of them. For each of these signals half of the signal transmission or storage capacity is thus used during half a line period. The picture information per period in the time-division multiplex encoded signal is sequentially composed of the time-compressed first and the time-compressed second luminance information. The relevant pictures may be used for the purpose of three-dimensional television in which one picture is intended for the left eye and the other picture is intended for the right eye. In this case both picture signals are supplied by the data receiver after time decompression or expansion. The transmitted or stored picture data utilizing the same transmission or data storage channel may also relate to entirely different pictures. Due to the time compression the two picture signals cannot be combined and supplied as such by the data receiver, that is to say, the receiver is to be able to select one or the other picture signal with the aid of a suitable indentification information. This transmission or storage system results in a loss of definition in view of the bandwidth limitation emanating from the compression and the decompression.
The invention is based on the recognition that the flexibility of the known television system can be even better utilized without too much loss of picture quality. To this end a television system according to the invention is characterized in that the encoding circuit is suitable for supplying at its output a time-division multiplex encoded signal having at least two sub-signals in which a first luminance information in the sub-signal supplied during the first part of a line period of the data generator corresponds to the luminance information of part of a line period of the first signal source and in which a second luminance information in the sub-signal supplied during the second part of the line period of the data generator corresponds to the luminance information of part of a line period of the second signal source, said signals being supplied after a change or no change in duration, the signal compression or expansion time ratio of the signal comprising the first luminance information differing from the corresponding ratio of the signal comprising the second luminance information, said ratio indicating the ratio between the durations of a luminance information before and after a change in duration, the decoding circuit being suitable for consecutively supplying during a line period of the data receiver a signal comprising luminance information which largely corresponds to the first luminance information, and a signal comprising luminance information which largely corresponds to the second luminance information.
Due to the measure according to the invention both sub-pictures with different time ratios for signal compression or expansion are transmitted or stored. Upon display the horizontal resolution of one sub-picture is therefore higher than the horizontal resolution of the other sub-picture. The more transmission or storage time is available for a sub-picture, the higher the horizontal resolution of this sub-picture and the lower the horizontal resolution of the other sub-picture. Thus it is obvious that a better quality of the first-mentioned sub-picture is at the expense of the quality of the second sub-picture. Consequently a choice has to be made between the two sub-pictures on the side of the data generator. For the sub-picture which is considered to be most important a high resolution may be given because little signal compression takes place whereas a lower resolution suffices for the other sub-picture because more signal compression is used. The above-defined time ratio is inverse to the above-mentioned time-compression factor. If this ratio is equal to 1:1, there is no signal compression and no signal expansion, whereas a ratio of more than 1:1 involves a signal compression and a ratio of less than 1:1 involves a signal decompression or expansion.
The television system according to the invention is also suitable for transmitting or storing colored images. A television system in which the signal from the first signal source and the signal from the second signal source also comprise chrominance information components, the encoding circuit being also suitable for a time-division multiplex encoding of the said signals with chrominance information and the decoding circuit being also suitable for supplying signals comprising chrominance information which largely corresponds to the data produced by the signal sources in the data generator is characterized in that in the time-division multiplex encoded signal applied to the output of the encoding circuit a first chrominance information during the said first part of a line period of the data generator corresponds to the chrominance information of the said part of a line period of the first signal source and that during the said second part of a line period of the data generator a second chrominance information corresponds to the chrominance information of the said part of a line period of the second signal source, the signal compression time ratio of the signal comprising the first chrominance information differing from the corresponding ratio of the signal comprising the second chrominance information, the decoding circuit being suitable for consecutively supplying during a line period of the data receiver a signal comprising chrominance information which largely corresponds to the first chrominance information, and a signal comprising chrominance information which largely corresponds to the second chrominance information.
A television system of this type is advantageously characterized in that the signal compression or expansion time ratio of the signal comprising the first luminace information is greater than the corresponding ratio of the signal comprising the second luminance information and that the signal compression time ratio of the signal comprising the first chrominance information associated with the signal comprising the first luminance information is greater than the corresponding ratio of the signal comprising the second chrominance information associated with the signal comprising the second luminance information.
A difference may also be made between the resolutions of the two sub-pictures in the vertical direction. A television system in which each chrominance information comprises two information components is characterized in that the first chrominance information is present during a number of line periods per field which is smaller than the number of line periods in which the first luminance information is present and that at least one information component of the second chrominance information is present during the number of line periods per field in which the second luminance information is present.
A data generator suitable for use in a television system according to the invention in which the encoding circuit includes a multiplex circuit for receiving the luminance information components from the signal sources and for generating the time-division multiplex encoded signal, said multiplex circuit comprising a switching stage controllable by means of a switching signal for selecting between the two signal sources, and a circuit for changing the duration for processing the luminance information is characterized in that the circuit for changing the duration is controllable by means of the switching signal for switching the signal compression or expansion time ratio between the first and the second part of a line period.
A data receiver suitable for use in a television system according to the invention, in co-operation with a data generator of the above-mentioned type, in which the decoding circuit includes a circuit for changing the duration for processing the received luminance information is characterized in that the circuit for changing the duration is controllable by means of a second switching signal for switching the signal compression or expansion time ratio between a first part of a line period of the data receiver in which the signal comprising luminance information which largely corresponds to the first luminance information is supplied and a second part in which the signal comprising luminance information which largely corresponds to the second luminance information is supplied.